1. Field of the Invention
The present invention relates to an image reading device having a platen with a black portion and a white portion.
2. Description of the Related Art
Image reading devices are used, for example, as input devices in facsimile apparatuses and in computers. The image reading devices include a housing having a reading station therein, a light source for irradiating an original (such as printed paper) bearing information thereon with light, and an image sensor receiving the light reflected by the original for reading the information on the original to produce an image. The image sensor is typically formed by an array of CCD elements. The irradiated light is reflected by the upper surface of the original and the image sensor can thus read the information on the upper surface of the original.
A platen is arranged at the reading station in the housing of the image reading device. The platen is usually formed by an entirely white plate or white colored metal. Alternatively, the platen is sometimes formed by an entirely black plate or black colored metal. If a white platen is used and when a relatively thin original bearing information on both surfaces thereof is inserted into the image reading device, a portion of the irradiated light is reflected by the upper surface of the original but another portion of the irradiated light passes through the original and reflected by the upper surface of the platen. The light reflected by the upper surface of the platen again passes through the original and reaches the image sensor with the result that information on the lower surface of the original is also read by the image sensor. Therefore, the information from both surfaces of the original appears when the image is produced, as shown in FIG. 20 of the attached drawings. In FIG. 20, the characters "1, 2, 3, 4, . . . " show information carried by the upper surface of the original and the characters "A, B, and C" show information carried by the lower surface of the original.
A black platen can solve this problem because the portion of the irradiated light that passes through the original is not reflected by the upper surface of the platen. However, the region of the platen outside the original is also read as if the black surface is information, and a black area 101 appears around the image of the original 100, as shown in FIG. 21. Such black area on the image could be removed by monitoring a display and using a mouse in a computer application, for example.